Harmonix announced Rivals last month during E3, but didn’t provide any details on what the $29.99 expansion would contain. While convincing people to pony up for new features is a tall order, Harmonix may be up to the task. Like any good expansion, Rock Band Rivals is about giving players more of Rock Band 4, as well as a better Rock Band 4. The add-on contains two parts: a goofy new story-based career mode, and, in a first for the series, an asynchronous multiplayer offering that's both cooperative and competitive.